Refrigeration units are conventionally known that are provided in refrigerated vehicles for transporting refrigerated food products, such as frozen food products, by land and cool their refrigerated compartments (see, for example, Patent Document 1). The refrigeration unit includes a sub-engine different from a driving engine for driving a refrigerated vehicle and an electric compressor driven by the sub-engine and is mounted on the bed of the refrigerated vehicle.    Patent Document 1: Published Japanese Patent Application No. H05-38933